Grid lead assembly



Dec. 23, 1941. H. J. DAILEY GRID LEAD ASSEMBLY Filed Jan. 18, 1941 INVENTOR .silicate glass l4. anode has a similar feather edge, not shown, sealed into a cylinder of borosilicate glass through which pass the cathode connections Patented Dec. 23, 1941 GRID LEAD ASSEMBLY Hampton J. Dailey, Bloomfield, N. .L, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania.

Application January 18, 1941, Serial No. 375,003

11 Claims.

My invention relates to discharge devices, and especially to the control grid lead-in of such devices.

An object of the invention is to provide an electrode connection to a vacuum-tight discharge device that will not put any undue strain on the seals, and the usual glass parts of such devices.

Other objects and advantages of the invention will be apparent from the following description and drawing in which:

Fig. 1 is a view principally in cross section of a discharge device to which my invention has been applied.

Fig. 2 is an enlarged view on lines II--II of Fig. 1.

Figs. 3 and 4 are cross-sectional views on lines III-III and IVIV, respectively, of Fig. 2.

One of the problems in connection with discharge devices, and especially to high power vacuum tubes, has been that of suitable lead-in connections to the electrodes on the interior of the devices. This is especially true where a very low resistance path is desired from the electrode structure to the exterior of the discharge device, as in devices utilizing heavy high frequency currents whereby even a small resistance causes a big loss.

The structures of the prior art that necessitated screw-threaded connections, for example, have caused considerable shrinkage in the construction of these tubes by the undue strain placed upon the seal and glass parts of the tube when such screw-threaded joints were made sufiiciently tight.

As previously stated, it is one of the objects of my invention to provide such a lead-in connection, particularly to the control electrode structure that will not place any undue strain upon the more delicate parts of the tube structure.

In Fig. 1 I have disclosed a type of discharge device to which my invention is adapted. This discharge device has a cathode it], generally comprised of tungsten wires, enclosed in a grid structure II, which is generally of a cylindrical cage of wires enclosing the cathode filaments. The anode I2 is an exterior electrode of copper in the form of a cylinder having at one edge a feather edge [3, sealed into a cylinder of boro- The bottom portion of the and l6.

Shields I1 and [8 are provided to shield the feather edge portions as is well known. My invention in this figure is applied to the electrical connection to the grid I l. The cylinder of borosilicate glass I4 has a reentrant cylinder portion 20 of less diameter and is sealed at a reduced portion 2| to the feather edge 22 of a copper thimble 23. This copper thimble 23 at its inner portion 24 is clasped by one or more bands 25, binding the grid standards 26 extending downward to the discharge space surrounding the cathode 10. These grid standards 26 form the electrical connections supports and also act as grid structure in combination with the wire bands 21 encircling them. A shield 28 is screwthreaded to the metal portion of the thimble 23 and extends around the seal of the glass 2| to the feather edge 22.

Considerable shrinkage has been caused by a necessarily tight screw-threaded connection being made to the interior of the thimble 23 to form a low resistance exterior connection thereto. This type of tube utilizes very heavy high frequency currents applied to the grid. These currents travel mainly through the outer surface or skin of the metal and a slight gap will cause large resistance losses. Such a screw-threaded tight connection has produced an undue strain on the seal of the feather edge 23 to the glass 2|, with the result that the seal has cracked and spoiled the tube.

It will also be noted that the deep recesses of the insulating structure makes rather difficult any other type of connection to the thimble after the tube has been assembled. My preferred embodiment, however, permits such an easy connection to the thimble without any undue strain on the seal or glass portions of the device.

As disclosed in Fig. 2, my preferred embodiment comprises a long cylinder of copper 30, having at its lower end exterior screw threads 3| to fit into the screw threads 32 on the interior surface of a thickened mid-portion 33 of the copper thimble 23. In order that there may be no diificulty in lightly screw-threading the cylinder 30 into the threads 32, I provide one or more slots or splits 34 in the end portion of this cylinder 30, as illustrated in Fig. 1.

The end of the copper tube 39, upon which the threads 31 are formed, is tapered on the inside at 35 with the taper making a rather thin edge 36 to the tube 30. I place on the interior of this portion of the tube a copper plug 31, having a taper corresponding to the taper 35.

This plug 31 has a preferably screw-threaded connection 38 to a bolt 39, extending to a slender bar Gil, supported on an interior shoulder 4| inside the tube 39. The slotted head :12 of the bolt 39, in combination with the screw-threaded connection 38 to the plug 31, provides means for adjusting the plug 31 to force the threads 3! on the end of the tube '39 into a Very tight engagement with the threads 32 on the interior portion of the thimble 23.

When it is desired to insert the grid connection 3!], the plug 3'5 is loosened in position so that the end of the tube can be lightly screwed into the interior of the thimble in the position illustrated in Fig. 1.

The bolt 39 is then revolved by a long screwdriver inserted in the slot in the bolt head 42, and the tapered plug 31 pulled up to force the screw threads 3| in tight engagement with the screw threads on the thimble.

The force exerted by this adjustment is lateral, and there is no twisting action upon'the thimble itself that would damage the feather edge seal between the thimble and the glass.

My grid connection also permits adequate cooling of the thimble adjacent the seal. A plurality of openings 43, such as three or more annular rows as disclosed in Figs. 1 and 2, provide passageways for a cooling medium from the inside of the tube 39 to be directed at the portion 44 of the thimble adjacent the feather edge 2i. The upper row of openings directs a stream directly at the seal. Any convenient cooling means, such as the fan 55 diagrammatically illustrated, can be used to direct the cooling medium, such as air, through the pipe Bil, openings 43, and out between the pipe and reentrant glass part 20. The bar 50 has been made as slender as possible so as not to interfere with the cooling medium.

Other types of expanding means may be utilized in place of the specific embodiment disclosed, and my specific expanding means can be used with other types of connections besides that of screw threads. In View of the many modifications that may be made, I desire only such limita tions to be imposed upon my invention as are necessitated by the spirit and scope of the following claims.

I claim:

1. A discharge device comprising an envelope containing electrodes therein, a reentrant portion of said envelope having an exposed'metal cylindrical surface, a hollow metal member having a dilatable portion making electrical contact with said exposed metal cylindrical surface, and dilating means within said hollow metal member for forcing said member into tighter engagement with said surface whereby rotative moment and the electrical contact resistance between said surface and said member is reduced to a minimum.

2. A discharge device comprising an envelope containing electrodes therein, a reentrant portion of said envelope having an exposed metal cylindrical surface, a hollow metal member having a dilatable portion making electrical contact with said exposed metal cylindrical surface, and a second member having a telescopic dilating fit with said first mentioned hollow metal member for forcing said first member into tighter engagement with said surface whereby rotative moment and the electrical contact resistance between said surface and said first mentioned member is reduced to a minimum.

3. A discharge-device comprisinganenvelope containing electrodes therein; a reentrant portion of said envelope including an annular metal portion having exposed screw threads, a metal tube having an end with screw threads making a screw thread joint with the screw threads on said metal portion, the screw-threaded end of said tube being split.

4. A discharge device comprising an envelope containing electrodes therein, a reentrant portion of said envelope including an annular metal portion having exposed screw threads, a metal tube having an end with screw threads making a, screw thread joint with the screw threads on said metal portion, the screw-threaded end of said tube being split, and means for expanding the screw threads on said tube into tight engagement with the screw threads on said metal part.

5. A discharge device comprising an envelope containing electrodes therein, a reentrant portion of said envelope including an annular metal portion having exposed screw threads, a metal tube having an end with screw threads makinga screw thread joint with the screw threads on said metal" portion, the screw-threaded end of said tube-being split, and means for expanding the screw threads on said tube into tight engagement with the screw threads on said metal part comprising a tapered plug at the end of said tube and means to adjust said plug.

6. A discharge device comprising an envelope containing electrodes therein, a metal thimble sealed to said envelope and projecting within said envelope, one of said electrodes supported on the projecting portion of said thimble, screw threads on the exposed inner surface of said thimble,-a tube having a screw-threaded end making a'connection with the screw threads of said thimble, said screw-threaded end being split.

7. A discharge device comprising an'envelope containing electrodes therein, a metal thimble sealed to said envelope and projecting within said envelope, one of said electrodes supported on the projecting portion of said thimble, a tube having a screw-threaded end making a connection with the screw threads of said thimble, said screwthreaded end-beingsplit, and means for expanding the screw threads on said tube into tight engagement with the screw threads on said metal thimble.

8. A discharge device comprising an envelope containing electrodes therein, a metal thimble sealed to said envelope and projecting within said envelope, one of said electrodes supported on the projecting portion of said thimble, a tube having a screw-threaded end making a connection with the screw threads of said thimble,- said screwthreaded end being split, and means for expanding the screw threads on said tube into tight en gagement with the screw threads n said'metal thimble comprising a tapered plug in the endof said tube and means to draw said plug alongthe axis of said tube to expand the split end of the tube.

9. A discharge device comprising anenvelope containing electrodes therein, a -metal thimble sealed to said envelope and projecting within said envelope, one of said electrodes supported on-the projecting portion of said thimble, a tube having a screw-threaded end making a connection with the-screw threads of said thimble, said screwthreaded end being split, and means for expanding the screw threads on said tube into tight-engagement with the screw threads on said-metal thimble comprising a tapered plug in the end of said tube and means to draw said plug'along the axis of said tube to expand the split end of the tube, the inner side of the end or the tube being tapered to correspond with the plug.

10. In combination with a discharge device having a hollow metal lead portion, a hollow thin walled metal member with an end portion, the interior of which is tapered and which is threadably connected to the interior of said metal lead portion, means for tightening said connection comprising a tapered plug inside of said member and engaging said interior tapered portion, and means for causing longitudinal movement of said plug to expand said tapered portion and tighten the threaded connection.

with said surface to improve the electrical conductance therebetweeen.

HAMPTON J. DAILEY. 

